Sounds like a dry joint somewhere. Have you looked underneath?
We won't be fixing A1200's I don't think, but, ask around at http://www.amigaworld.net
someone may meet you there and have a look at it for you. We are having an Amiga Medic area, you could try your luck there. Or alternatively, I am sure someone will have A1200's for sale (second hand) for little money in our bring and buy area.